1. Field of the Invention
This invention relates to a prosthetic implant having a photocatalytic layer adapted to fight periprosthetic infection.
2. Description of the Related Art
It is well known that infections occur in about 1% to about 5% of all primary arthroplasties, and that “the economic impact, the morbidity, and the emotional trauma of prosthetic joint infection is immense and devastating to the patient and society”. Trampuz et al., Clin. Orthop., (414), 2003 pp. 69-88. It is believed that a majority of these infections occur via transmission from microbes upon the surgical gloves, the patient's skin, implants or instruments. Unlike routine systemic infections, infections associated with implants (“periprosthetic infections”) are particularly troublesome.
It has been reported that certain biomaterials cause an abnormal and inferior immune response. In short, a portion of the immune response is provided by the release of superoxide ions, such as hydroxyl radicals, that are lethal to microbes. However, when a periprosthetic infection occurs, it has been reported that biomaterials such as cobalt chrome alloys cause abnormal neutrophil activity, resulting in an inferior non-productive immune response. Shanbhag, J. Biomed. Mar. Res., Vol. 26, 185-95, 1992.
It appears that the presence of the implant surface helps the microbes survive both the immune response and antibiotic treatment. In particular, microbes of concern attach to the implant surface and form a polymer-like glaze (or “biofilm”) between themselves and the local environment. This biofilm acts as an effective barrier to both neutrophils and antibiotics.
Although the periprosthetic infection itself is a primary concern for the patient, it is also known that the immune response triggered by the body to fight the infection also results in bone loss. In particular, the increased phagocyte concentration also increases the local concentration of tumor necrosis factor (TNF-α). The TNF-α concentration in turn upregulates the local level of osteoclasts. These increased osteoclast concentration uncouples the normal balance in bone metabolism, thereby leading to localized bone loss. This localized bone loss may result in the loosening of the implant, thereby necessitating its removal.
U.S. Pat. No. 6,503,507 (“Allen”) discloses the use of a light-activated composition that produces singlet oxygen. Allen discloses that the singlet oxygen produced therefrom is effective in killing bacteria. U.S. Pat. No. 6,527,759 (“Tachibana”) discloses the use of light activated drugs that produce singlet oxygen.
Implant Sciences Corp. has promoted a surface treatment for percutaneous medical devices that prevents the growth of bacteria by employing the germ-fighting properties of silver coatings. U.S. Pat. No. 6,592,888 (“Jensen”) discloses the use of metallic compounds in wound dressings to produce anti-microbial effects. U.S. Pat. No. 6,605,751 (“Gibbins”) discloses the use of silver containing anti-microbial hydrophilic compositions. US Patent Application 20030204229A1 (“Stokes”) discloses the use of a polymeric casing containing cations as biologically active agents to be used on medical implants and devices.
Ohko, J. Biomed. Mat. Res. (Appl Biomat) 58: 97-101, 2001 reports coating titania upon silicone catheters and medical tubes, and illuminating those tubes with UV light. Ohko further reported the bactericidal effect of the subsequent photocatalysis on E. coli cells. However, Ohko states that TiO2 is toxic under illumination, and that because the part of the TiO2 coating buried in the patient's body can not be illuminated, the coating should not be harmful to the body. Therefore, it appears that Ohko discourages the in vivo irradiation of titania.
US Published Patent Application 2003/0125679 (“Kubota”) discloses a medical tube comprising an elastomer and a photocatalyst layer, wherein the tube has excellent antibacterial activity.
Trepanier, J. Biomed. Mat. Res. (Appl Biomat) 43, 433-440 (1998) reports providing an oxide layer of less than 1000 angstroms upon a NiTi cardiovascular stent.